Supersonic radar trainer signal reflecting prism and altitude ring suppressor



June 13, 1950 w. H. BAKER 2,510,947'

SUPERSONIC RADAR TRAINER SIGNAL REFLECTING v PRISM AND ALTITUDE RINGSUPPRESSOR Filed Aug. 18, 1947 2 Sheets-Sheet 1 INVENTOR. w/L; mw H.Eff/(51 June 13, 1950 W. H. BAKER SUPERSONIC RADAR TRAINER SIGNALREFLECTING PRISM AND ALTITUDE RING SUPPRESSOR Filed Aug. 18, 1947 2Sneets-Shet 2 INVENTOR. WM L MN ff ,5w/5e patented .Furie 13, 1959sprsasonro arman 'manana sionistasrL'so'riNG raisin D Amir-Ups RINGsnrranssoa ttilliL-mnii.A Baker, Daytony @hio application angustia1947;'seria1No. 769,285*

3- Claims.

(Granted under the act of March; 3 1883, as. amended April 3G, 1928;3704 0.V G.. 75,79;

Theiinvention described hereinV may be manu'.- factured and used by orfor the Government. for governmental purposes without payment to me ofany royaltythereon.

This invention relates to radar. equipment and more particularly to amodified.radar training equipment inclusive of a particular prism foruse as a part thereof and inclusive of means for minimizing altitudering phenomena from equipment presentations. Y

In training: students in radar operationsland presentations, agroundtraining equipmentsimf ulating ield radar operations is `commonly. used.In the form of such equipment to which the presentvinvention pertains, aradar antenna asa semblyiissimulated by a trolleyfmounted rotate ablepipe closed at its lower end by a quartz crys-f tal and carrying asignal reilecting prism suspended below the lower end of the pipe. Thelower end of the pipe and the prism are immersed in a tank of water.Radar synchronizing signal from a usual radar set is modified andapplied to the quartz crystal. These signals set up sound waves in thewater that simulate both the signal presentation and the echo thereofupon the screen of a cathode ray tube part' of' the radar set. The prismimmersed in the Water and' spaced from the lower end of the pipereflects both `f thesignalirom .the quartzcrystal and the signal echoreturned to the quartz crystal from t l 1eYV bottom oi" the tank uponwhich a contour manmay be disposed, if preferred.

Presentations in such equipment have been characterized heretofore byaltitude ringsthat appear upon a PPI presentation as a series ofconcentric circles appearing upon the radar scope orscreen of a cathoderay tube. These rings are objectionable since they occur in the vicinityof the bomb release marker spaced by the distance. between the soundgenerator or crystal inthe lower end of the pipe and the bottom of thetank: orrelief map.

The present invention comprises essentiallya prism having a signalreflecting face or a predetermined configuration for optimum signal andecho reiiection in combination with sound absorbent pads secured uponhorizontally disposed parts of the assembly that are positioned tointercept echo signals from the bottom of the tank and that server tosubstantially eliminate or to minimize altitude rings as spurious signalpresentations.

An objectof4 theIv present invention isto provide improved radartraining equipment of in creased similarity to -eld equipment and char-2 l acterizedr bysfpresentationslthat are substantially free from.altitude ring interference.`

Anotherl objectlis to providea-signal reflecting pris-m a f or f the 1designatedi equipment that has an optimum reecting face ofmathematic'ahy de terminedconguration;

AJ furtherY obiect` -is--. toprovide meansk inl the designated.Iequipment for suppressing altitude rings,

With .theaboveand other obj 'eots-inY-v-iewWl-iicl will be apparent-fromthef following description anlillustrative@apparatus err-ibociyingl thepresent invention is .shown in" the accompanying-L dravve ings wherein:

Eig. l. is a fragmentary side elevationalV View partly. in section. ofa`rada-r simulating sou-rrdK generaton assembly that embodies 7 theinvention and'. that; issuspended upon' atrolle-yf to'l'ie-Inovi ablyimmersed in a tank of water;

Eig` 2.y isA ani: elevationalV` vieweoff thel assembly shown. in Fig.V ltaken 'from theeri-ght sid'e'theijee Fig- .ais atplan' viewffrom-belewofthe *device shown inFi-gs. l and 2';`A and' Eig; 4- isia graphvillustrating:the'derivationofy the signal reflecting: face of# aVprisr'n that '-isa partei ithe;r assembly shown in Fig; l:

Anillustrative apparatirsltofw-hichY `the -pes'ent invention is :appliedis-shovvr1 in the accompany-A ing. drawings* ande comprises a rotatablesou-ridnl generator immersed'in a'- tanieof Water:

The sound l generator shown comprises a' pipe l. havingaaquartz crystal2-`mount`ed^in- 'its' lvvei' end inv a-'pla-neunormal to ther-axisofthe-p et The. quartz crystal# -2 is #the Anucleus l or 'thel sup r2'son-ic system fo simulating amada-1 picture 'iii'a,.supersonicftrainer:` 'Ihefcrystal 2 isidispdsd substantial-lyparallel Avte :the-bottomoiitlre'tank* 3, tank4 contains arsoundtransmitt fluid su-ch as water Ii." Acentral signal conduct.- ingrodextends axially'and'centrally of tliep jeji l lwhich' serves l as ashie1de1ectrode-ioi 'fa cdaxial, cable with me rod 'ses theCentraieondueters The conducting. vvrod i. is supported centrally Iofthe pipe I lby aiplyuralijtyl or". polystyrene spacerst)The-proditterminatesfatitslovverend inta; socket into which-,anpintlsupported by jan exten-il nallygthr-.eaded polystynen'e spacer xseats:tdm'ake an; electrical. .-conneetioni therewith. Y The;Y polyi--styrenespacer `B'xtlireads into,l the lower: end/of; the?` pipe VI asshown. The1pin11 carries,-afcatr'sivvhisa` ker;v 9; theavvenend` ofwhich contactsrthe' upprerrl' face of Athe-crystalci Bothuthe uppersan'dlowerf faces-of. thecrystal iiare splattered Withmetalli's gold.vHL,

The crystal 2 is mounted upon the lower end of the pipe i by a centrallyapertured metal cap II that threads thereupon. The cap II terminnatesupwardly in a preferably substantially flush flange I2 that is knurledor provided with wrench lands for turning it with respect to the pipe I.A thin lead gasket I3 is interposed between the cap II and the goldspattered lower face of the crystal 2.

The assembly connections are made water tight by the use of paraiiin orthe like. The cap II has a flat ear I5 to which a prism reference plateI6 is secured by welding or the like so that it extends beyond the endof and substantially parallel with the axis of the pipe II. The flat earI5 is apertured for a pin 20 upon which the upper end of a prismcarrying plate 2I is movably mounted. Plate 2| is secured to a flat sideof the prism I'I with water impervious cement. A spring 22 is interposedbetween the plate I6 and the plate 2l under compression against theadjustable action of a screw 23 that has a knurled head and that is usedfor setting the prism face I8 with respect to signals radiated from thecrystal 2 into the water 4.

The altitude ring suppressing embodiment of the present inventioncomprises a resilient covering of rubber, cork, resilient plastic or thelike cemented or otherwise secured to overlie horizontally disposedsurfaces exposed to the water 4. As shown, the horizontally disposedlower face of the cap II has a ring 25 of rubber or the like cementedthereto. A plate 26 of a like material is cemented to and overlies thelower and horizontally disposed face of the prism Il and of the loweredge of the prism carrying plate 2|. A strip 2l of correspondingmaterial is positioned to overlie the lower edge of the prism referenceplate I6.

With this assemblage, a large part of or all of the horizontallydisposed surfaces, other than the crystal 2, that are exposed to signalsconducted Iby the water il are protected from vertical forcedistribution components that set up altitude rings in the radar setpresentations.

The sound absorbent ring 25, plate 26 and strip 2l are attached andsecured to the cap II, prism I'I and plate 2l, and to the referenceplate I6 respectively with water insoluble cement. Preferably allhorizontally disposed surfaces against which sound waves having avertically directed force component would strike are cushioned in thedescribed manner in order to eiectively remove objectionable altituderings from the radar signal presentations at the reproducer of the radarset. Toward this end the wrench land bearing or knurled ange I2 on thecap lI for use in turning the cap I I on the pipe I, preferably bearscushioning material on its lower side if it projects radially outwardlyfrom the cap II, although preferably it is provided with a knurledperipheral surface that is flush with the remainder of the cap I I.

The entire pipe assembly is adapted for rotation in synchronism with therotation of the radar antenna with which the presently disclosedequipment is used for test purposes.

In the derivation of the reflecting face I8 of the prism Il, asindicated in Fig. 4 of the accompanying drawings, alpha is defined asthe angle at which sound intensity is incident to the horizontal planeof the relief map or to any point terminate in the horizontal plane. Theangle alpha may be measured from a reference point beyond the axis. Thevertical leg of the angle 4 alpha is measured along the Y axis and thehorizontal leg along the X axis. The angle alpha is a variable dependingupon the point on the curve of the prism face I8 at which a tangent isdrawn thereto.

A wave emanating from the crystal 2 strikes the curve of the prism facei8. Sound energy emanating from the crystal is considered as acollimated source due to its changed wave length. This energy, as ithits the reflector or prism face I8, breaks up into an infinite numberof sound sources distributed over the face of the reflecting prism faceI8. Each infinitesimally small point on this reflector is considered asan original source of energy. The curvature of the reflecting prism faceI8 is such that these innitesiinally small units of energy are sent outto an infinite number of targets distributed along the horizontal planeof the map 38 so as to affect an even distribution of energy over themap for any given range which has been predetermined in the design ofthe prism face I8. The target from which these innitesirnally smallunits of energy are reflected is determined by a tangent to the curve atthat particular point of reflection. The slope of the curve is Fromwhich SO-beta is equal to alpha Hence the equation for the curve of thereflecting face IB of the prism I'I is:

d y o alpha) dx-tan beta) tan 45 -2 The curve so determined has beenfound experimentally to provide satisfactory signal performance.

Because of the rapidity with which signal is applied to the quartzcrystal 2 it is not -known technically whether the quartz crystalvibrates in single waves of maximum amplitude at the center of thecrystal or in a multiplicity of minute waves radiating from the centerto the peripheral edge of the crystal, which in effect would appear as asine wave. In any event, it is known that the described assemblyfunctions to simulate with practical satisfaction the field operationsof a. radar set in the transmission and reception of signals when thecurve of the prism face I8 is so derived. Error of the training systemitself with respect to ground range is minimized by starting the topportion of the reflector curve of the prism face I8 as close to thecrystal 2 as is possible, taking into consideration the construction ofthe crystal holder or cap Ii and the support for the prism II.

From a production standpoint it is necessary that the prism I1 beadjustably mounted with respect to the crystal 2. In production the Yaxis .of the prism Il ,may b e variable about a `pivot at the topthereof in order that limitations rin mechanical production of thedevice may be Ybetween .the fao@ of the crystal 2 and the prism face I8.

In using the trainer a megacycle pulse of one microsecond duration istransmitted tothe crystal l2 under water through a matching circuit,.not shown. Energy is directed in a vertical plane from the crystal 2 tothe glass reflector prism face i3 mounted directly beneath it. Thecurvature of the signal reflecting prism face is varies in such a manneras to simulate the cosecant squared distribution pattern of the basicradar equipment. .fis previously stated, it is assumed that the soundenergy is reflected by the prism face I8 in such a manner that the angleof incidence is equal to the angle of reflection. The emitted signalafter being reflected by the prism face I8 is transmitted to the maplinbuilt in relief and mounted on the bottom of the tank Ii under water.Refiected sound energy is transmitted by the water d to the reflectorprism face I8 where it is reflected to the crystal 2. Again the signalYincident angle is assumed to be equal to the reflected angleretransmitted to the quartz crystal 2. The quartz crystal 2 is vibratedmechanically by the returned echo signal so received, thereby setting upan electrical signal in the cats Whisker S proportional to the intensityof the echo signal return and from there it is passed to the rada-requipment.

The radar training set with which the present device is used has been:developed as an advanced operational radar trainer for radar operatorsof the PPI indicating type of radar equipment and presentation. It isused for the instruction of students in radar and more particularly theinterpretation oi radar signals in navigation bombing and iconoscopeinterpretation wherein practice is needed in reading presentations upona cathode ray tube. Patent No. 2,405,591, issued August 13, 1946, toWarren P. Mason, for Training device, discloses a related equipment.

The pipe I which contains the crystal 2 is a mechanical means ofimmersing the crystal 2 in the water li, so that it may be rotated insynchronism with the radar antenna. The reflecting prism face i8 may beadjusted to increase or decrease the over-all signal range distributionby means of the set screw 2S which is mounted at the lower end of thereflector assembly. The whole assembly including crystal 2 andreflecting prism Il is mounted upon a bridge assembly or trolleymechanism not shown, so that it may be varied in altitude above the map3l! by operation of the mechanism to which the central pipe is mounted.This mechanism is suspended above the tank of water on a bridge assemblythat is generally referred to as a trolley mechanism.

Operatively the radar equipment, not shown, which is basic to the systemdevelops a pulse of one microsecond duration which is used as a basicsynchronizing signal, as previously inferred. This vsignal is passedthrough a coaxial cable to a 15 imegacycle signal generator. A onemicrosecond 15 megacycle pulse is developed within thissgnalgeneratorand passed through a matchingcircuit to a coaxial cable which matchesthesignal to a matching circuit mounted on the trolley mecha- Ilsrn. Fromthere this signal is transmitted downthe centerconductor `50i the pipe Ito thecrystal 2 through the pin 'l andthe cats Whisker 9. Thiselectrical energy is transferred into mechanical Yvibration due to thepiezoelectric quartz crystal 2 which develops a Small wave length soundwave which travels in a straightdirection. This ,SOundl wave is directeddownward to the glass reflector prism face I8 Vfrom whence the signal isnreilecteclthrough the water 4 in the tank 3 to the profile map 30 fromwhich it is returned as an echo signal to the prism face I8.

The reflected signal is `distributed from a range directly below thecrystal 2 `to a maximum range equivalent to 50 miles in an illustrativetrainer. The curvature of the crystal face IS is continuously varying insuch a manner as -to accomplish .this result. The curvature directs thereiiected energy so that the incident ray of sound energy is reflectedat the saine angle to which it contacts the reflector curve. After theenergy has been reflected from the reliector face I8 it is transmittedthrough the water `ll to the relief map-3l) from which the energy isreflected back along the same course to the same point on the reectorface I3 from which it started.

This energy is then reflected directly upward to the quartz crystal 2.The resultant mechanical vibration of the crystal 2 develops anelectrical voltage proportional to the amount of energy returned. Thissignal is then transmitted back along the coaxial cable conductor 5through the matching network to a high frequency amplifier and thence tothe radar circuitry for presentation in a usual manner, where it isidentified as an echo signal resulting from the previously transmittedsignal.

The bridge assembly or trolley mechanism that has been referred tohereinabove is a device by means of which the pipe and thc reflectingassembly carried at the lower end of the pipe may be moved frequently inlateral direction over the relief map 3o exposed upon the bottom of thewater tank 3. The scale of the map is at a ratio between sound waves andthe speed of light or radio Waves. A transmitted signal of onemicrosecond :duration may result in an echo that is returned to thepiezoelectrical crystal 50 microseconds after the application of thetransmitted signal to the same crystal 2. This delay is adequate tominimize or eliminate the interference between the transmitted signaland the echo signal when the presently disclosed equipment is used. Thesignal attenuation is in the order 67 decibels permitted in signaltransmission through water.

The ground training apparatus modified as indicated herein providespresentations to the students that more nearly approach the actual radarsignal and echo presentations observed in radar operations in the fieldthan has been possible with any comparable piece of equipment knownheretofore. The presentations from equipment that embodies the presentinvention are of improved precision and reality, due to the prism faceI8 that is disclosed herein, and that are substantially free fromaltitude ring interference due to the absorption of vertically directedsound waves by the rubber cushioning pads that form parts 0f the presentinvention and that also are disclosed herein.

It 'is to be lunderstood that the form of the invention that is shownand described herein has been submitted as being illustrative of asuccessfully operating embodiment of the invention and may be modifiedwithin limits within the scope of the present invention.

What I claim is:

1. A prism for use in reflecting sound in radar training equipment andhaving a reflecting face of curvature defined by the equation %=tan 45+y where alpha is the angle at which sound intensity is incident to anypoint terminate in a horizontal plane and beta is the angle ofreflection of Sound incident to the reflection face of the prism;

2. In an operator training radio detection and ranging system equipmentwherein electrical radio signal is converted into mechanical vibrationsignal for conduction through a fluid medium and back into an electricalsignal, comprisingV a hollow pipe adapted for making ground Contact withthe fluid, a gold splattered quartz crystal closing the lower end ofsaid pipe against the entrance of iiuid thereinto and having a goldsplattered face insulated from said pipe, a ,central rod Within saidpipe and electrically insulated therefrom, a central rod contactengaging the gold splattered face of said quartz crystal insulated fromthe said pipe, and a mechanical vibration signal reflecting curved prismface of adjustable angularity with respect to the axis of said pipe andsecured thereto in suspension from the sealed `crystal carrying endthereof.

3. In an operator training radio detection and ranging system equipmentwhereby electnical radio signal is converted into mechanical Vibrationsignal for conduction through a iiuid then back into electrical signal,comprising a hollow pipe, and electrically conductive rod extendingwithin and axially substantially centrally of said pipe, insulatingmeans maintaining said rod sub- @tan (90 been Vstantially centrally ofsaid pipe, a pin mounted at an end of said rod and continuing axiallythereof,

Number "a cats Whisker carried by theunattached endof said pin,` aninsulating spacer threading into an end of said pipe and supporting theunattached end of said pin, an apertured flanged cap thread- `ing uponthe end of said pipe within which the `insulating spacer is threaded, aquartz crystal quartzcrystal, a prism reference plate mountedl rigidlyto depend from said apertured cap, a

prism carryingplate hingedly mounted with respect to said prismreference plate, spring means urging said priism carrying plate awayfrom said prism reference plate, an adjustable set screw rotatablymounted in said prism reference plate and-said prism carrying plate forcausing the hinged adjustable separation thereof against the yieldingresistance of said spring, prism means mounted on to move with saidprism carrying plate and having a fluid conducted mechanical Vibrationreflecting face disposed normally in angular relation with respect tosaid quartz plate, a fluid conducting mechanical Vibration dampeningrubber pad attached to said prism remote from and substantiallyfparallel to said quartz crystal, and a fluid conducted mechanicalVibration dampening rubber strip on the edge of said prism referenceplate remote from its attached end and substantially parallel to saidquartz crystal.

WILLIAM H. BAKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date 2,405,591 Mason Aug. 13, 1946

